Sonar buoys deployed in continued search for Flight 370

(CNN) – The search for Malaysia Airlines flight 370 has search crews using all kinds of technology to find the missing plane. The latest detection of an underwater signal came from sensors designed for US Navy combat.

They’re dropped out of a plane, plummet into the sea with a parachute, descend below the surface, open up their payload, and hunt for their target. These aren’t bombs or torpedoes, they’re called Sonobuoys.

“Sonobuoys are essentially a sensor package that’s parachuted out of the aircraft, floats on the surface of the ocean and will deploy a hydrophone.” said Commodore Peter Leavy of the Royal Australian Navy.

An Australian defense source tells CNN it was Sonobuoys that detected the latest, possibly man-made signal in the search area. They were dropped from an Australian P-3C Orion plane.

Capt. Van Gurley, a former Navy oceanographer, told CNN “And once it hits the water surface, then it’s got some saltwater switches that start activating different deployments. Everything that’s in this canister starts to unwind. There’s a bunch of gear in there that’s packed in very nicely. Some of it floats to the surface so there’s a radio-antenna that talks to the aircraft so the buoy and the aircraft are constantly in communication, and then the microphones, the hydrophones actually listening for the signals on a very long string. And they deploy below the canister.”

The Australians got this batch from American manufacturers, who sent a cargo plane to Indiana in recent days to pick up more than a thousand Sonobuoys. The device was first tested and deployed by the u-s navy, but not for this purpose.

“In anti-submarine warfare this is one of the tools the Navy has to look for and track enemy submarines. So they’re under the ocean surface. They don’t have a radar signature and you need to use sound and smart waves- both actively and passively- to find them and then track them.”

On this mission, the Sonobuoys and the Orion planes deploying them have been modified to detect sounds in the frequency-range of black box pings. Sonar-operators on board the aircraft are manning computers to receive and analyze the signals.

Sonobuoys are dropped in a pattern 84 of them at a time, and have a shorter range to detect signals than the towed pinger locator, but they’re durable.

“The beauty of these things, the sonobuoys, once you put ’em out- they stay out there for a long time: up to 8 hours.”

Then they expire, and sink to the bottom.

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